Stigma, cohesion and HIV outcomes among vulnerable women across epidemic settings Female sex workers (FSW) are at significantly heightened risk for HIV. Globally, FSW have a 13.5 times greater odds of being HIV-infected compared to women who are not sex workers. Despite this burden, less than half of FSW have access to antiretroviral therapy (ART). HIV stigma is a critical social determinant known to negatively influence HIV outcomes including access to treatment and ART adherence. For FSW living with HIV, the impact of HIV stigma may be further compounded by other forms of stigma related to their occupation, gender, and/or socioeconomic position. In response to such stigmas, FSW in many settings have come together in solidarity to address the socio-structural context of their HIV-related risk. Social cohesion within the sex worker community has been a central element of community-based responses to HIV and is significantly associated with protective behaviors. However, the role of social cohesion, and its potential mediating influence on HIV and sex work stigma, has yet to be explored in relation to HIV treatment outcomes. While significant attention has been paid to the measurement of HIV stigma in past studies, much less emphasis has been placed on other intersecting social stigmas, including the measurement of sex work stigma. Utilizing the existing research infrastructure of two ongoing cohorts located within distinct social and epidemic settings, we propose to longitudinally examine the role of HIV and sex work stigma and social cohesion as key social determinants of HIV outcomes among FSW living with HIV in Tanzania and the DR. Our specific aims are to: (1) Develop a valid and reliable aggregate measure of sex work-related stigma tailored to the realities of FSW living with HIV in distinct social and epidemic contexts; (2) Determine the roles of HIV and sex work stigma and social cohesion as predictors of biologic HIV outcomes (e.g. ART in the blood, viral suppression) across settings; and (3) Qualitatively explore the dynamic context of HIV and sex work- related stigma and social cohesion among FSW in relation to HIV services and outcomes. For Aim 1 we will use qualitative methods to inform measurement development including both in-depth and cognitive interviews (n=40). We will then employ IRT and factor and reliability analysis to establish shared and distinct items related to the domain of sex work stigma per context. In Aim 2, we will conduct longitudinal structural equation modeling to examine predictors and pathways between HIV and sex work stigma, social cohesion and viral suppression in the context of other known correlates of viral suppression among cohorts of FSW living with HIV in Tanzania and the DR (n=400). In Aim 3 will explore the dynamic social context of HIV and sex work stigma and social cohesion through longitudinal qualitative in-depth interviews among a subset of cohort participants in each country (n=40). Findings will inform tailored treatment as prevention interventions among FSW across geographic and epidemic settings.